Dissecting the function of the DNMT2-homolog (DNMA) in Dictyostelium discoideum

Methylation of cytosine residues in nucleic acids plays a critical role in a range of biological activities in eukaryotes, including regulation of transcription, organization of chromatin structure, modulation of translation, cellular differentiation, and development. While much of the scientific focus in this field was centered on DNA methylation over the past few decades, it has also become clear that methylation of RNA is a crucial modification. A group of homologous DNMT2 methyltransferase enzymes in different model organisms are now known to catalyze the transfer of a methyl group to the cytosine at position 38 in tRNAAspGUC molecules. The important biological role for tRNA methyltransferases is highlighted by the fact that the genomes of some model eukaryotes, including Dictyostelium discoideum, Drosophila melanogaster, Entamoeba histolytica, and Schizosaccharomyces pombe, possess a DNMT2 homolog but do not encode any other enzymes of the DNMT family. In this study, we explore the function of the DNMT2 homolog (DNMA) in D. discoideum by examining the phenotypic effects resulting from deletion of this enzyme. Pleiotropic impacts on cell growth, morphology and motility, nuclear organization, and disruption to the developmental program are detected. We also analyze global gene expression in the dnmA knock-out cells and develop a homology-based structural model of DNMA, allowing us to perform docking simulations of the molecular interaction with tRNAAspGUC. Our findings demonstrate that DNMA, as a tRNA methyltransferase, is critical to normal cellular activity and development in Dictyostelium.